NUCLEATION LAYERS FOR ENHANCING PHOTOCATALYTIC ACTIVITY OF TITANIUM DIOXIDE (TiO2) COATINGS

ABSTRACT

A photocatalytic system having enhanced photo efficiency/photonic efficacy is provided that includes a thin nucleation material coated on a substrate. The nucleation material enhances lattice matching for a subsequently deposited photocatalytic active material. Such a photocatalytic system may be used as a self-cleaning surface in an application where removal of fingerprints and other residue is desired. In certain aspects, the nucleation material comprises aluminum oxide (Al 2 O 3 ) and the photocatalytic material comprises an anatase phase of titanium dioxide (TiO 2 ) deposited over the nucleation material. A photocatalytic activity of the system is ≥about 50% above a comparative photocatalytic activity where the photocatalytic active material is disposed directly on the substrate. Methods of making such photocatalytic systems are also provided.

INTRODUCTION

This section provides background information related to the presentdisclosure which is not necessarily prior art. The present disclosurerelates to enhancing photocatalytic activity of titanium dioxide (TiO₂)by use of a nucleation layer that provides lattice matching to promoteformation of desirable phases of TiO₂ having enhanced photocatalyticactivity, such as anatase TiO₂. Methods of making TiO₂ having enhancedphotocatalytic activity are also provided.

Various surfaces may come into contact with skin, such as touch screens,glasses, windows, camera lenses, appliances, mirrors, and the like. Whensuch surfaces are touched by an animal, fingerprint oil and/or otherorganic residues can remain that are highly visible. Thus, it would bedesirable to develop an active surface layer for such surfaces thatserves to remove oil residue. TiO₂ may be used to catalyze a degradationreaction of oil or other organic residues on a surface by absorbing UVlight and water from the atmosphere to release free radicals that reactwith and degrade the oil residues. It would be desirable to enhance thecatalysis reaction to expedite degradation and removal of oil andorganic residues from such a surface.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In certain aspects, the present disclosure relates to a photocatalyticsystem that may include a nucleation material coated on a substrate. Thenucleation material comprises a metal oxide compound, where the metal isselected from the group consisting of: aluminum, zirconium, niobium,cerium, vanadium, lanthanum, titanium, silicon, iron, cobalt, nickel,molybdenum, tungsten, and combinations thereof. A photocatalytic activematerial comprising an anatase phase of titanium dioxide (TiO₂) isdeposited over the nucleation material. A photocatalytic activity of isgreater than or equal to about 50% above a comparative photocatalyticactivity where the photocatalytic active material is disposed directlyon the substrate.

The photocatalytic system may further include the nucleation materialhaving an average thickness of less than or equal to about 10 nm.

The photocatalytic system may further include the nucleation materialbeing selected from the group consisting of: aluminum oxide (Al₂O₃),SrTiO₃ (STO), LaAlO₃ (LAO), Y stabilized ZrO₂ (YSZ), and combinationsthereof.

The photocatalytic system may further include the nucleation materialincluding aluminum oxide (Al₂O₃). In certain aspects, the aluminum oxide(Al₂O₃) comprises a θ-Al₂O₃ phase having a monoclinic space group withlattice parameters of a=1.185 nm, b=0.295 nm and c=0.562 nm.

The photocatalytic system may further have a lattice mismatch of lessthan or equal to about 12% between the nucleation material and thephotocatalytic active material.

The photocatalytic system may further include the active material havinggreater than or equal to about 50% by volume of anatase phase.

The photocatalytic system may further include the photocatalyticactivity being greater than or equal to about 75% above the comparativephotocatalytic activity where the active material is disposed directlyon the substrate,

In other aspects, the present disclosure provides a self-cleaningphotocatalytic system including a substrate, a nucleation coatingincluding aluminum oxide (Al₂O₃) disposed on the substrate having athickness of less than or equal to about 10 nm, and an exposed surfacecomprising a photocatalytic active material that includes an anatasephase of titanium dioxide (TiO₂) deposited over the nucleation coating.The photocatalytic active material facilitates a decomposition reactionof any oil or organic residue on the exposed surface when in thepresence of water and ultraviolet radiation.

The self-cleaning photocatalytic system may further include theself-cleaning photocatalytic system's photocatalytic activity beingabout 50% above a comparative photocatalytic activity where thephotocatalytic active material is disposed directly on the substrate.

The self-cleaning photocatalytic system may further include thenucleation coating having an average thickness of greater than or equalto about 3 nm to less than or equal to about 5 nm.

The self-cleaning photocatalytic system may further include thephotocatalytic active material including greater than or equal to about50% by volume of the anatase phase of titanium dioxide (TiO₂).

The self-cleaning photocatalytic system may further include thesubstrate comprises glass or an anti-reflection coating.

The self-cleaning photocatalytic system may further include the exposedsurface defining a plurality of islands of the photocatalytic activematerial distributed within a low surface energy polymeric material,where the nucleation coating is disposed beneath the photocatalyticactive material, but is absent in the regions where the low surfaceenergy polymeric material is present.

The self-cleaning photocatalytic system may further include a latticemismatch is less than or equal to about 2% between the nucleationmaterial and the photocatalytic active material.

The self-cleaning photocatalytic system may further include the aluminumoxide (Al₂O₃) including a θ-Al₂O₃ phase having a crystal structurehaving a monoclinic space group with lattice parameters of a=1.185 nm,b=0.295 nm and c=0.562 nm that enhances lattice matching and formationof the anatase phase of titanium dioxide (TiO₂).

In yet other aspects, a method of enhancing photocatalytic activity in aphotocatalytic system includes depositing a nucleation material coatedon a substrate. The nucleation material includes a metal oxide compound.The metal is selected from the group consisting of: aluminum, zirconium,niobium, cerium, vanadium, lanthanum, titanium, silicon, iron, cobalt,nickel, molybdenum, tungsten, and combinations thereof. The methodfurther includes depositing a photocatalytic active material includingan anatase phase of titanium dioxide (TiO₂) over the nucleationmaterial, wherein the nucleation material provides lattice matching toenhance formation of the anatase phase of titanium dioxide (TiO₂), sothat a photocatalytic activity is greater than or equal to about 50%above a comparative photocatalytic activity where the photocatalyticactive material is disposed directly on the substrate.

The method may further include the depositing of the nucleation materialbeing a process selected from the group consisting of: atomic layerdeposition (ALD), chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (CVD), physical vapor deposition (PVD), andcombinations thereof.

The method may further include the depositing of the photocatalyticactive material being a process selected from the group consisting of:atomic layer deposition (ALD), chemical vapor deposition (CVD),atmospheric pressure chemical vapor deposition (APCVD), low pressurechemical vapor deposition (LPCVD), plasma enhanced chemical vapordeposition (CVD), physical vapor deposition (PVD), magnetron sputtering,wet chemistry, sol-gel processes, and combinations thereof.

The method may further include depositing of the nucleation material isdone by an atomic layer deposition process and the nucleation materialhas a thickness of less than or equal to about 10 nm.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 shows a sectional side view of a photoactive system including asubstrate, a nucleation layer, and a photoactive layer prepared inaccordance with certain aspects of the present disclosure.

FIG. 2 shows a sectional side view of a photoactive system including asubstrate that is an anti-reflection layered coating, a nucleationlayer, and a photoactive layer prepared in accordance with certain otheraspects of the present disclosure.

FIG. 3 shows a sectional side view of a photoactive system including asubstrate and a self-cleaning surface that includes islands of anucleation material and photocatalytic active material disposed within alow surface energy material prepared in accordance with yet otheraspects of the present disclosure.

FIG. 4 shows a comparative chart of photocatalytic activity forMethylene Blue (absorbance versus time) of a photoactive system preparedin accordance with certain aspects of the present disclosure compared toa control and a comparative sample lacking a nucleation layer.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific compositions, components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, elements, compositions, steps, integers, operations, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. Although the open-ended term “comprising,” is tobe understood as a non-restrictive term used to describe and claimvarious embodiments set forth herein, in certain aspects, the term mayalternatively be understood to instead be a more limiting andrestrictive term, such as “consisting of” or “consisting essentiallyof.” Thus, for any given embodiment reciting compositions, materials,components, elements, features, integers, operations, and/or processsteps, the present disclosure also specifically includes embodimentsconsisting of, or consisting essentially of, such recited compositions,materials, components, elements, features, integers, operations, and/orprocess steps. In the case of “consisting of,” the alternativeembodiment excludes any additional compositions, materials, components,elements, features, integers, operations, and/or process steps, while inthe case of “consisting essentially of,” any additional compositions,materials, components, elements, features, integers, operations, and/orprocess steps that materially affect the basic and novel characteristicsare excluded from such an embodiment, but any compositions, materials,components, elements, features, integers, operations, and/or processsteps that do not materially affect the basic and novel characteristicscan be included in the embodiment.

Any method steps, processes, and operations described herein are not tobe construed as necessarily requiring their performance in theparticular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed, unless otherwiseindicated.

When a component, element, or layer is referred to as being “on,”“engaged to,” “connected to,” or “coupled to” another element or layer,it may be directly on, engaged, connected or coupled to the othercomponent, element, or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly engaged to,” “directly connected to,” or “directlycoupled to” another element or layer, there may be no interveningelements or layers present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.). As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various steps, elements, components, regions, layers and/orsections, these steps, elements, components, regions, layers and/orsections should not be limited by these terms, unless otherwiseindicated. These terms may be only used to distinguish one step,element, component, region, layer or section from another step, element,component, region, layer or section. Terms such as “first,” “second,”and other numerical terms when used herein do not imply a sequence ororder unless clearly indicated by the context. Thus, a first step,element, component, region, layer or section discussed below could betermed a second step, element, component, region, layer or sectionwithout departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,”“inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and thelike, may be used herein for ease of description to describe one elementor feature's relationship to another element(s) or feature(s) asillustrated in the figures. Spatially or temporally relative terms maybe intended to encompass different orientations of the device or systemin use or operation in addition to the orientation depicted in thefigures.

Throughout this disclosure, the numerical values represent approximatemeasures or limits to ranges to encompass minor deviations from thegiven values and embodiments having about the value mentioned as well asthose having exactly the value mentioned. Other than in the workingexamples provided at the end of the detailed description, all numericalvalues of parameters (e.g., of quantities or conditions) in thisspecification, including the appended claims, are to be understood asbeing modified in all instances by the term “about” whether or not“about” actually appears before the numerical value. “About” indicatesthat the stated numerical value allows some slight imprecision (withsome approach to exactness in the value; approximately or reasonablyclose to the value; nearly). If the imprecision provided by “about” isnot otherwise understood in the art with this ordinary meaning, then“about” as used herein indicates at least variations that may arise fromordinary methods of measuring and using such parameters. For example,“about” may comprise a variation of less than or equal to 5%, optionallyless than or equal to 4%, optionally less than or equal to 3%,optionally less than or equal to 2%, optionally less than or equal to1%, optionally less than or equal to 0.5%, and in certain aspects,optionally less than or equal to 0.1%.

In addition, disclosure of ranges includes disclosure of all values andfurther divided ranges within the entire range, including endpoints andsub-ranges given for the ranges.

Example embodiments will now be described more fully with reference tothe accompanying drawings.

In various aspects, the present disclosure provides a photoactive systemthat may be a self-cleaning system 20. The self-cleaning system 20includes a substrate 22 having a nucleation material coating 24 coatedthereon as shown in FIG. 1. A photoactive layer 26 comprises aphotocatalytic active material. The photocatalytic material 34 mayprovide an exposed surface 28 with self-cleaning capability. It shouldbe noted that the nucleation material coating 24 and photoactive layer26 may also form discrete regions on the exposed surface 28 rather thana continuous layer, as will be described further below. Thephotocatalytic active material in the photoactive layer 26 may oxidizeand/or vaporize any organic material, e.g., squalene, present on theexposed surface 28, as set forth in more detail below. In particular,the photocatalytic active material may be a photocatalyst that isactivated upon exposure to certain wavelengths of ultraviolet radiation,for example, visible light or ultraviolet light. Visible light haswavelengths ranging from about 390 to about 750 nm, while ultravioletlight has wavelengths from about 10 nm to about 390 nm.

For example, where the photoactive layer 26 of the self-cleaning system20 is exposed to UV radiation, for example, having a wavelength belowapproximately 357 nm, in the presence of water (e.g., ambient humidity),the photocatalytic active material, e.g., TiO₂, is activatedfacilitating a photocatalytic reaction. A photocatalytic reaction maycreate an oxidation agent that breaks down the organic matter, e.g.,squalene or other organic materials, to low chain hydrocarbons to carbondioxide and water in the presence of the photocatalyst, electromagneticradiation, e.g., ultraviolet light; and water, e.g., humidity fromambient conditions. As such, the photocatalytic active materialaccelerates a rate of the photocatalytic decomposition reaction.

By way of further detail, when electromagnetic radiation having adesired wavelength illuminates the photocatalytic active material in thephotoactive layer 26, an electron from the valence band of thephotocatalytic active material may promote to the conduction band of thephotocatalytic active material, which in turn may create a hole in thevalence band and an excess of negative charge or electron in theconduction band. The hole may promote oxidation and the electron maypromote reduction. Generally, the hole may combine with water to producea hydroxyl radical (.OH). The hole may also react directly with squaleneor other organic material to increase an overall self-cleaningefficiency of the self-cleaning system 20. Similarly, oxygen in theambient environment surrounding the photocatalytic active material maybe reduced by the electron to form a superoxide ion (.O₂ ⁻), which inturn may oxidize the organic material present on the exposed surface 28of the self-cleaning system 20. In certain aspects, reaction byproductsmay volatilize or otherwise be removed from the self-cleaning system 20.

In addition, the hole may become trapped before recombination with theelectron. For such situations, the photocatalytic active material may befunctionalized, for example by doping. The dopants may act as anelectrocatalyst and may increase a transfer of electrons to oxygenmolecules, which may in turn lower the occurrence of the recombinationof electrons and holes.

Therefore, the self-cleaning system 20 may be characterized asself-cleaning so that the substrate 22 is protected from residue byremoving, e.g., oxidizing and/or vaporizing the fingerprints, squalene,oils, and/or organic material deposited by touch of an operator.Consequently, the self-cleaning system 20 may enhance aesthetics,cleanliness, and readability of reflective or transparent surfaces fordisplay systems, lenses, sensors, and the like.

In certain aspects, a source of electromagnetic radiation may beprovided near the self-cleaning system 20 to direct light having apredetermined range of wavelengths at the photoactive layer 26 of theself-cleaning system 20. Alternatively or additionally, theself-cleaning system 20 may also be heated, for example by infraredradiation, to improve diffusion of the organic materials to facilitatereaction with photocatalytic active material in the photoactive layer26.

Suitable photocatalytic active materials may include, but are notlimited to, photo-oxidative semiconductors, semiconducting oxides, dopedmetal oxides, heterojunction materials, and combinations thereof. In oneembodiment, the photocatalytic active material may be titanium dioxide(TiO₂) and may comprise an anatase phase, which may exhibit acomparatively higher photocatalytic activity than a rutile form of TiO₂.Tetragonal anatase TiO₂ has lattice parameters of c=0.951 nm and a=0.378nm. As described below, where the photocatalytic active materialcomprises TiO₂, while the amount of anatase is desirably maximized, theTiO₂ may be may be present as a combination of the rutile form and theanatase form.

Further, the photocatalytic active material may be doped to form afunctionalized photocatalytic material, for example, a functionalizedtitanium dioxide. By way of example, the functionalized photocatalyticactive material may be doped with a metal such as, but not limited to,palladium, ruthenium, silver, chromium, cobalt, copper, vanadium, iron,silver, platinum, molybdenum, lanthanum, niobium, and combinationsthereof. Alternatively, the functionalized photocatalytic material maybe doped with a non-metal such as, but not limited to, nitrogen, sulfur,carbon, boron, potassium, iodine, fluorine, and combinations thereof.

In other non-limiting embodiments, the photocatalytic active materialmay include a semiconducting oxide such as, but not limited to, zincoxide, bismuth, tin oxide, and combinations thereof. The semiconductingoxide may be selected to have a band gap separation suitable for aphotocatalytic reaction, as set forth in more detail below.

The nucleation material coating 24 serves to enhance lattice matching ofa subsequent active material layer comprising titanium dioxide (TiO₂)deposited thereon. More specifically, the nucleation material coating 24promotes formation of desirable crystal structures with small latticemismatch and phases of the photocatalytic active material subsequentlydeposited in the photoactive layer 26 over the nucleation materialcoating 24. In one variation, an anatase phase of the photocatalyticactive material TiO₂ exhibits enhanced photocatalytic activity ascompared to other phases of TiO₂, such as rutile or brookite phases. Thelattice spacing presented by the nucleation layer 24 to the growing TiO2film serves to promote anatase formation.

The nucleation layer 24 also substantially matches the surface energy ofanatase TiO₂ for initiating the film growth at low temperatures below400° C., optionally at greater than or equal to about 200° C. to lessthan or equal to about 350° C., and in certain aspects, optionally at350° C.

In certain aspects, the photoactive layer 26 may comprise titaniumdioxide, where greater than or equal to about 50% by volume of thetitanium dioxide is present an anatase phase, optionally greater than orequal to about 60% by volume, optionally greater than or equal to about70% by volume, optionally greater than or equal to about 80% by volume,optionally greater than or equal to about 90% by volume, and in certainvariations, optionally greater than or equal to about 95% by volume ofthe titanium dioxide is present an anatase phase.

In certain variations, the photoactive layer 26 may have an averagethickness of less than or equal to about 50 nm, optionally less than orequal to about 25 nm, optionally less than or equal to about 20 nm,optionally less than or equal to about 10 nm, optionally less than orequal to about 9 nm, optionally less than or equal to about 8 nm,optionally less than or equal to about 7 nm, optionally less than orequal to about 6 nm, and in certain variations, optionally less than orequal to about 5 nm. The photocatalytic activity of anatase TiO₂increases with thickness nearly exponentially, saturating at about 5 nm,thus in certain variations, the average thickness may be about 5 nm toabout 7 nm thick. It should be noted that the photoactive layer 26 isnot limited to such dimensions and may indeed have a thickness abovethose listed above.

The nucleation material coating 24 may be thin, for example, having anaverage thickness of less than or equal to about 10 nm, optionally lessthan or equal to about 9 nm, optionally less than or equal to about 8nm, optionally less than or equal to about 7 nm, optionally less than orequal to about 6 nm, and in certain variations, optionally less than orequal to about 5 nm. In certain aspects, the nucleation material coating24 may have an average thickness of greater than or equal to about 3 nmto less than or equal to about 10 nm, optionally greater than or equalto about 3 nm to less than or equal to about 5 nm.

In certain aspects, the nucleation material coating 24 comprises a metaloxide compound having a crystal lattice structure with a lattice spacingthat promotes growth of an anatase film during deposition. The latticetemplate of the nucleation material coating 24 is believed to promoteformation and growth of the anatase TiO₂ phase at lower temperaturesthan are might otherwise be required. In certain aspects, the nucleationmaterial coating 24 optimizes oriented nucleation growth required forthe crystallinity and lattice matching with anatase TiO₂ while providinghigh adhesion and minimum stress. The metal oxide used as the nucleationmaterial in the nucleation material coating 24 may comprise a metalselected from the group consisting of: aluminum, zirconium, niobium,cerium, vanadium, lanthanum, titanium, silicon, iron, cobalt, nickel,molybdenum, tungsten, and combinations thereof.

In certain variations, the nucleation material coating 24 comprisesaluminum oxide or alumina (Al₂O₃) as the nucleation material. Where thenucleation material coating 24 comprises Al₂O₃ it may have a crystallattice structure of a monoclinic space group with lattice parameters ofa=1.185 nm, b=0.295 nm and c=0.562 nm. An advantageous nucleationmaterial coating 24 comprises a high percentage of the θ-Al₂O₃ phase. Incertain aspects, the nucleation material provides lattice matching withthe photocatalytic material deposited thereon. In certain aspects, suchlattice matching can be understood to be a lattice mismatch between thenucleation material coating 24 and the photoactive layer 26 of less thanor equal to about 15%, optionally less than or equal to about 12%,optionally less than or equal to about 10%, optionally less than orequal to about 8%, optionally less than or equal to about 5%, optionallyless than or equal to about 4%, optionally less than or equal to about3%, optionally less than or equal to about 2%, and in certainvariations, optionally less than or equal to about 1%.

In other variations, epitaxial growth of anatase can also be promoted bySrTiO₃ (STO), LaAlO₃ (LAO), and Y stabilized ZrO₂ (YSZ) nucleationlayers. STO has a cubic symmetry with a lattice parameter of a=0.39.Thus, STO has a similar lattice matching, with a mere mismatch of only3.04% to the lattice of the growing anatase film. LAO is rhombohedralwith lattice parameters of a=0.536 nm and c=1.311 nm. LAO presents amismatch of only about 11.6% to the lattice of growing anatase film. YSZis cubic with a lattice parameter of a=0.514 nm.

The nucleation material coating 24 may be deposited on the substrate 22by atomic layer deposition (ALD), chemical vapor deposition (CVD),including atmospheric pressure chemical vapor deposition (APCVD), lowpressure chemical vapor deposition (LPCVD), plasma enhanced chemicalvapor deposition (CVD), physical vapor deposition (PVD), such asmagnetron sputtering, wet chemistry, such as dip, spray or sol-gelprocesses, or other techniques known for depositing thin layers of metaloxides, such as Al₂O₃. In certain aspects, the metal oxide nucleationmaterial coating 24 may be applied by an atomic layer deposition (ALD)process that can coat a substrate with a conformal layer that comprisesthe metal oxide layer, such as aluminum oxide (Al₂O₃). ALD is aself-limiting process for chemical deposition or growth of ultra-thinfilms on a substrate. The ALD chemical gas-phase thin film depositionmethod is advantageous mainly for the surface-controlled andself-saturating monolayer formation, which can create ultrathinconformal structures coating all surfaces of the substrate in acontinuous film. ALD typically involves subjecting the target substrateto self-saturating surface reactions. For an aluminum oxide (Al₂O₃)coating, a precursor selected from the group consisting of: trimethylaluminum (TMA ((CH₃)₃Al)), triethyl aluminum ((C₂H₅)₃Al), diethylaluminum ((C₂H₅)₂AlCl), tributyl aluminum ((C₄H₉)₃Al), aluminum chloride(AlCl₃), aluminum ethoxide (Al(OC₂H₅)₃), aluminum isopropoxide(Al(C₃H₇O)₃), aluminum fluoride (AlF₃), aluminum nitride ((AlN), wherethe precursor is TMA and ammonia), and the like. Precursors for formingother metal oxide coatings described above via ALD and ALD reactionconditions are further described in U.S. Pub. No. 2015/0162602 toDadheech et al., the relevant portions of which are hereby incorporatedby reference.

ALD is typically conducted in an apparatus having a vacuum depositionchamber with a holder for the substrate, at least one vapor source(known as the precursor) and various controls by which the substrate maybe individually subjected to the vapor source. Such controls may includeheaters, coolers, flow routing and valves, for controlling the amount ofexposure of the substrate to the vapor source. The regions of thesubstrate to be coated may be pre-treated, for example, by plasmatreatment. The ALD process for deposition of surface coating onto thesubstrate involves reaction of the surface in a deposition chamber witha single vapor of precursor materials or reaction of the surface withmultiple vapors introduced sequentially and having the precursors of thesurface coating. Suitable precursors may include organic and inorganicmetallic compounds. The vapor may be pulsed into the vacuum depositionchamber on a carrier gas and may be quickly purged, for example, byvacuum pumping or flushing with an inert gas. Such pulsing of the vaporand purging of the system may be performed to control the dose of theprecursor vapor to which the substrate is exposed.

Generally, the ALD process is performed at elevated temperatures andreduced pressures. Temperature of the deposition chamber is desirablyhigh enough that reaction between the substrate and the precursors inthe vapor occurs, while also preventing condensation of the vapor ontothe surface. As non-limiting examples, the reaction space in thedeposition chamber may be heated to between about 50° C. and about 800°C., and the operating pressure may be between about 7.5×10⁻² Torr andabout 4 Torr (about 1 Pa to about 5000 Pa).

As a result of ALD process and surface reactions, a single atomic layerof the surface coating material is bound to substrate surface, therebyproviding a monoatomic coating. With sequential or alternatingreactions, composite layers may be formed. Furthermore, additionalatomic monolayers may be grown over the monoatomic layer, therebyforming a surface coating having greater thicknesses. The ALD process isillustrative of one technique for forming aluminum oxide (Al₂O₃)coatings on a substrate, but the process may also be used to form othercoatings as well, by way of non-limiting example. For example, otheroxide-based based coatings may be formed on the substrate via an ALDprocess. Moreover, various other coatings can be easily obtained byusing different precursors and deposition processes.

In certain variations, the first vapor precursor may comprise aluminum.As a non-limiting example, the first vapor precursor may be selectedfrom a group consisting of trimethyl aluminum (TMA ((CH₃)₃Al)), triethylaluminum ((C₂H₅)₃Al), diethyl aluminum ((C₂H₅)₂AlCl), tributyl aluminum((C₄H₉)₃Al), aluminum chloride (AlCl₃), aluminum ethoxide (Al(OC₂H₅)₃),aluminum isopropoxide (Al(C₃H₇O)₃), aluminum fluoride (AlF₃), aluminumnitride ((AlN), where the precursor is TMA and ammonia). The secondvapor precursor may comprise water vapor or a plasma. Suitable plasmasfor ALD include argon (Ar), hydrogen (H₂), oxygen (O₂), nitrogen (N₂),and combinations thereof.

In one variation, the ALD process employs a first vapor precursor oftrimethyl aluminum (TMA (CH₃)₃Al) and/or aluminum chloride (AlCl₃) andwater vapor (H₂O) as a second vapor precursor, which forms aluminumoxide (Al₂O₃).

The photoactive layer 26 may be deposited on the nucleation materialcoating 24 by atomic layer deposition (ALD), chemical vapor deposition(CVD), including atmospheric pressure chemical vapor deposition (APCVD),low pressure chemical vapor deposition (LPCVD), plasma enhanced chemicalvapor deposition (CVD), physical vapor deposition (PVD), such asmagnetron sputtering, such as magnetron sputtering or radiofrequency(RF) sputtering, or other techniques known for depositing photocatalyticactive materials, like titanium dioxide having an anatase crystalstructure.

Where the titanium oxide (TiO₂) is applied via an ALD process, theprecursor materials may be titanium n-butoxide (n-C₄H₉O)₄Ti), titaniumt-butoxide (t-C₄H₉O)₃Ti), titanium chloride-aluminum chloride(TiCl₃.1/3AlCl₃), titanium (IV) chloride (TiCl₄), titanium (IV)isopropoxide (C₃H₇O)₄Ti), tetrakis(diethylamido)titanium(IV), and/ortetrakis(dimethylamido)titanium(IV), by way of example. Suitablenon-limiting precursors for forming a titanium oxide coating via ALDcomprise titanium tetrachloride (TiCl₄) and water (H₂O). For a titaniumoxide coating (TiO₂), the precursor materials may be titaniumtetrachloride (TiCl₄), tetrakis(diethylamido)titanium(IV),tetrakis(dimethylamido)titanium(IV), and/or titanium(IV) isopropoxide,by way of example. In one variation, suitable non-limiting precursorsfor forming a titanium oxide coating via ALD comprise titaniumtetrachloride (TiCl₄) and water (H₂O). In another variation, magnetronsputtering may be conducted, for example, by using a titanium metaltarget, RF magnetron sputtering from ceramic TiO₂ targets, or may bedirect deposition from a ceramic titanium dioxide target to form TiO₂photoactive material. In such deposition techniques, Ti atoms, O atoms,and TiO species all impinge upon the surface and skate around to findtheir lowest energy configuration within kinetic constraints. Where thenucleation material template is in place to promote a TiO₂ crystalconfiguration corresponding to anatase, then the surface will be coatedsubstantially with domains of anatase microcrystal.

Thus, in certain variations, a thin Al₂O₃ nucleation layer enhances thephotonic efficacy and photocatalytic activity of TiO₂-containing activecoatings. As noted above, the nucleation layer optimizes orientednucleation growth required for the crystallinity and lattice matchingwith high adhesion and minimum stress. Including the Al₂O₃ basednucleation layer significantly improves the growth of anatase phase ofTiO₂ enabling a high photocatalytic activity as compared to TiO₂ withoutthe nucleation layer.

In certain variations, the presence of the nucleation material on thesubstrate enhances the photocatalytic activity of the photocatalyticactive materials in the photoactive layer, as compared to thephotocatalytic activity of a photocatalytic active material depositeddirectly on the substrate in the absence of the nucleation materialcoating. For example, the photocatalytic activity for a system includingthe nucleation material disposed on the substrate (having a substrate, anucleation material, and a photoactive layer disposed thereon) inincreased by greater than or equal to about 50% as compared to thesystem lacking the nucleation material layer, optionally thephotocatalytic activity is greater than or equal to about 60% greater,optionally the photocatalytic activity is greater than or equal to about70% greater, and in certain variations, optionally the photocatalyticactivity is greater than or equal to about 75% greater. Thephotocatalytic activity can be measured by ISO standard 10678“Determination of Photocatalytic Activity of Surfaces in an AqueousMedium by Degradation of Methylene Blue” that measures temporalabsorbance changes of methylene blue when in contact with thephotocatalytic active material, such as TiO₂.

The substrate (e.g., substrate 22 in FIG. 1) may be formed of a varietyof different substrates. In certain variations, the substrate comprisessilicon dioxide (SiO₂), sodium borosilicate, soda-lime-silica glass, orother glasses. The substrate may be amorphous or crystalline. In certainaspects, the substrate may be formed of float glass. It should be notedthat due to the presence of the thin nucleation material coating, a highquality photoactive material layer can be formed on a variety ofsubstrates of varying quality, crystallinity, and surface roughness. Inother aspects, the substrate may be a multilayered structure, such as ananti-reflection coating, which may have multiple layers with distinctrefractive indices.

The substrate may be amorphous or crystalline. In certain aspects, thesubstrate may be formed of float glass. In other aspects, the substratemay be a multilayered structure, such as an anti-reflection coating,which may have multiple layers with distinct refractive indices.

Such a self-cleaning system 40 is shown in FIG. 2, where a substrate 42is in the form of an anti-reflection coating. By way of non-limitingexample, an anti-reflection coating may have alternating layers of highrefractive index material, like titanium dioxide (TiO₂), and lowrefractive index material, like silicon dioxide (SiO₂), with differentthicknesses. By using alternating layers of a low-index material likesilica and a higher-index material titania, it is possible to obtainreflectivity as low as 0.1% at a single wavelength. Such anti-reflectioncoatings can give very low reflectivity over a broad band.

In one embodiment, the antireflection coating may include a first layer44 of TiO₂ (a high refractive index material) having a thickness ofabout 10 nm, a second layer 46 of SiO₂ (a low refractive index layer)having a thickness of about 33 nm, a third layer 48 of TiO₂ having athickness of about 100 nm, and a fourth layer 50 of SiO₂ having athickness of about 75 nm. A nucleation material coating 52 may bedeposited or applied to the fourth layer 50 of the substrate 52 in theform of the anti-reflection coating. A photoactive layer 54 comprising aphotocatalytic active material may be deposited over the nucleationmaterial coating 52.

In other aspects, another self-cleaning system 60 is shown in FIG. 3,where a substrate 62 is also in the form of an anti-reflection coating.The antireflection coating may include a first layer 64 of TiO₂ (a highrefractive index material) having a thickness of about 10 nm, a secondlayer 66 of SiO₂ (a low refractive index layer) having a thickness ofabout 33 nm, a third layer 68 of TiO₂ having a thickness of about 100nm, and a fourth layer 70 of SiO₂ having a thickness of about 75 nm. InFIG. 3, a nucleation material coating 72 is disposed over discrete,non-contiguous, select regions of the fourth layer 70. A photoactivecoating 74 comprising a photocatalytic active material is disposed overthe discrete, non-contiguous, select regions where the nucleationmaterial coating 72 is disposed over the fourth layer 70.

A low surface energy material 76 is also disposed within select regionsof the fourth layer 70 and is disposed between the discrete,non-contiguous, select regions where the nucleation material coating 72and photoactive coating 74 are applied on the fourth layer 70. In thismanner, the nucleation material coating 72 and photoactive coating 74define distinct islands within the low surface energy material 76. Thelow surface energy material 76 may define a contact angle with water ofgreater than 110°, optionally greater than or equal to about 115°,optionally greater than or equal to about 120°, optionally greater thanor equal to about 125°, optionally greater than or equal to about 130°,optionally greater than or equal to about 135°, and in certainvariations, optionally greater than or equal to about 150°. As such,water, oils, and contaminants may effectively bead on and may be mobile,translating across an exposed surface 78 defined by the low surfaceenergy material 76 having the islands of photoactive coating 74 disposedtherein.

The low surface energy material 76 may be a fluoropolymer. By way ofnon-limiting example, the fluoropolymer may be a perfluorocarbonsiloxane. In one embodiment, the perfluorocarbon siloxane polymer is apolytetrafluoroethylene (PTFE) siloxane polymer. In certain aspects, thelow surface energy material 76 may be applied as a thin layer, forexample, as a monolayer having a thickness of one molecule.

A method of forming the self-cleaning system 60 may include depositing aperfluorocarbon siloxane polymer onto the substrate 62 in a continuouslayer. It should be noted that the substrate 62 need not be ananti-reflection multilayered coating as shown in FIG. 3. In one examplemethod, the nucleation material coating 72 and photoactive coating 74can be applied continuous films or layers. Then, photolithographicmethods can be used to pattern the layers of nucleation material coating72 and photoactive coating 74 to produce islands of photoactive coating74 separated by bare substrate 62. Before removal of the photoresistfrom atop the photoactive coating 74, the low surface energy material76, such as perfluorocarbon siloxane polymer, may be subsequentlydeposited. The may be deposited or coated onto the substrate 62 in anysuitable manner. By way of non-limiting examples, depositing of the lowsurface energy material may occur by chemical vapor depositing (CVD),atomic layer deposition (ALD), dipping, wiping, spraying, meniscuscoating, wet coating, combinations and equivalents thereof. Depositingmay include forming a self-aligned monolayer that is physicallyadsorbed, i.e., physisorbed, and cross-linked with neighboring moleculesthrough a siloxane moiety. After application of the low surface energymaterial 76, the photoresist can removed by dissolution to form aself-cleaning layer or film 80. Generally, the photocatalytic activematerial in the photoactive coating 74 may be present in theself-cleaning film 80 in an amount of from about 2 parts by volume toabout 35 parts by volume based on 100 parts by volume.

In certain aspects, the self-cleaning photocatalytic systems provided inaccordance with certain aspects of the present disclosure enabledisappearance or removal of visible fingerprints and other visibleresidue from an exposed surface, which is a function of UV flux. Theself-cleaning photocatalytic systems provided in accordance with certainaspects of the present disclosure enable disappearance or removal ofvisible fingerprints and other visible residue from an exposed surface(e.g., in an interior of a vehicle) in less than or equal to about 4hours, optionally less than or equal to about 3 hours, optionally lessthan or equal to about 2 hours, optionally less than or equal to about1.5 hours, optionally less than or equal to about 1 hour, optionallyless than or equal to about 45 minutes, optionally less than or equal toabout 45 minutes, and in certain variations, optionally less than orequal to about 20 minutes.

Various embodiments of the present technology can be further understoodby the specific examples contained herein. Specific Examples areprovided for illustrative purposes of how to make and use thecompositions, devices, and methods according to the present teachingsand, unless explicitly stated otherwise, are not intended to be arepresentation that given embodiments of this invention have, or havenot, been made or tested.

Example 1

Methylene Blue Degradation via the Photocatalytic Activity of TiO₂ Filmsby use of ISO Standard 10678—a Method for Quantifying PhotocatalyticActivity of Materials Using the Elimination of Solution Phase MethyleneBlue. As noted above, ISO 10678 specifies measuring temporal absorbancechanges of a methylene blue in contact with the material (TiO₂, in thisexample).

Experimental Conditions are as follows. A Methylene Blue (MB) solutionis provided in a column having a height of 50 mm. Aconcentration/initial absorbance is 0.74. A light source used is anultraviolet (UV) black light where irradiance is 4 mW/sq·cm.

A first Control sample labeled 110 has a float glass substrate on whicha titanium dioxide (TiO₂) layer is directly deposited via a MS,ALD/APCVD process. The Control 110 is maintained under the sampleconditions while disposed in the MB solution, but is not exposed to UV(dark sample). The ALD precursors for TiO₂ are TiCl₄ and/or titaniumisopropoxide.

A second comparative sample labeled 112 includes a TiO₂ film disposed ona float glass substrate. The TiO₂ layer is deposited via an atomic layerdeposition via ALD with the precursor above directly onto the substratesurface. The TiO₂ photoactive layer has an average thickness of about 10nm. It is believed that directly depositing the TiO₂ onto the glasssubstrate via ALD process creates a TiO₂ layer comprising a combinationof brookite, rutile, and minor amounts of anatase.

A third sample labeled 114 includes a nucleation layer comprising Al₂O₃disposed on a float glass substrate in accordance with certain aspectsof the present disclosure. The Al₂O₃ is deposited via an atomic layerdeposition with precursor described above and has a thickness of about 5nm. Under such conditions, it is believed that primarily a θ-Al₂O₃ phaseis formed. Then, a TiO₂ film is deposited over the Al₂O₃ via an ALDprocess directly onto the substrate surface. The TiO₂ photoactive layerhas an average thickness of about 10 nm. The amount of anatase formed inthe TiO₂ film over the Al₂O₃ template is significantly increased ascompared to the second comparative sample 112.

FIG. 4 shows time 100 versus absorbance 102 measuring Methylene Blue(MB) degradation via photocatalytic activity. 14% of the MB isdecomposed via photocatalysis by the TiO₂ on an alumina nucleation layerafter 4 hours as shown for Sample 114. By way of comparison, 8% of theMB is decomposed via photocatalysis by TiO₂ without an aluminanucleation layer after 4 hours for Sample 112. Therefore, use of anAl₂O₃ nucleation layer in Sample 114 increases the photocatalyticactivity of ALD grown TiO₂ films by about 75%.

Rate constants for the photocatalytic degradation of MB for the thirdsample labeled 114 and second comparative sample 112 are believed to beas follows. A pseudo first order rate constant for Sample 114 is4.97×10⁻⁴ mol/liter/s, whereas the rate constant for Sample 112 is3.44×10⁻⁴ mol/liter/s. Thus, under experimental conditions (light flux,MB pH, and temperature) the Al₂O₃ nucleation layer increases the rateconstant by a factor of about 1.45.

As such, the present disclosure provides excellent photocatalyticactivity for TiO₂ films due to the presence of a primer nucleation layerof Al₂O₃, which improves the c-axis crystal growth providing the desiredcrystallinity, texture and conformability of TiO₂ coatings. Such aprocess may be readily scaled and used in a continuous manufacturingprocess.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A photocatalytic system comprising: a nucleationmaterial coated on a substrate, wherein the nucleation materialcomprises a metal oxide compound, wherein the metal is selected from thegroup consisting of: aluminum, zirconium, niobium, cerium, vanadium,lanthanum, titanium, silicon, iron, cobalt, nickel, molybdenum,tungsten, and combinations thereof; and a photocatalytic active materialcomprising an anatase phase of titanium dioxide (TiO₂) deposited overthe nucleation material, wherein a photocatalytic activity is greaterthan or equal to about 50% above a comparative photocatalytic activitywhere the photocatalytic active material is disposed directly on thesubstrate.
 2. The photocatalytic system of claim 1, wherein thenucleation material has an average thickness of less than or equal toabout 10 nm.
 3. The photocatalytic system of claim 1, wherein thenucleation material is selected from the group consisting of: aluminumoxide (Al₂O₃), SrTiO₃ (STO), LaAlO₃ (LAO), Y stabilized ZrO₂ (YSZ), andcombinations thereof.
 4. The photocatalytic system of claim 1, whereinthe nucleation material comprises aluminum oxide (Al₂O₃).
 5. Thephotocatalytic system of claim 4, wherein the aluminum oxide (Al₂O₃)comprises a θ-Al₂O₃ phase having a monoclinic space group with latticeparameters of a=1.185 nm, b=0.295 nm and c=0.562 nm.
 6. Thephotocatalytic system of claim 1, wherein a lattice mismatch is lessthan or equal to about 12% between the nucleation material and thephotocatalytic active material.
 7. The photocatalytic system of claim 1,wherein the active material comprises greater than or equal to about 50%by volume of anatase phase.
 8. The photocatalytic system of claim 1,wherein the photocatalytic activity is greater than or equal to about75% above the comparative photocatalytic activity where the activematerial is disposed directly on the substrate.
 9. A self-cleaningphotocatalytic system comprising: a substrate; a nucleation coatingcomprising aluminum oxide (Al₂O₃) disposed on the substrate having athickness of less than or equal to about 10 nm; and an exposed surfacecomprising a photocatalytic active material that comprises an anatasephase of titanium dioxide (TiO₂) deposited over the nucleation coating,wherein the photocatalytic active material facilitates a decompositionreaction of any oil or organic residue on the exposed surface when inthe presence of water and ultraviolet radiation.
 10. The self-cleaningphotocatalytic system of claim 9, wherein a photocatalytic activity ofthe self-cleaning photocatalytic system is greater than or equal toabout 50% above a comparative photocatalytic activity where thephotocatalytic active material is disposed directly on the substrate.11. The self-cleaning photocatalytic system of claim 9, wherein thenucleation coating has an average thickness of greater than or equal toabout 3 nm to less than or equal to about 5 nm.
 12. The self-cleaningphotocatalytic system of claim 9, wherein the photocatalytic activematerial comprises greater than or equal to about 50% by volume of theanatase phase of titanium dioxide (TiO₂).
 13. The self-cleaningphotocatalytic system of claim 9, wherein the substrate comprises glassor an anti-reflection coating.
 14. The self-cleaning photocatalyticsystem of claim 9, wherein the exposed surface defines a plurality ofislands of the photocatalytic active material distributed within a lowsurface energy polymeric material, wherein the nucleation coating isdisposed beneath the photocatalytic active material, but is absent inthe regions where the low surface energy polymeric material is present.15. The self-cleaning photocatalytic system of claim 9, wherein alattice mismatch is less than or equal to about 2% between thenucleation material and the photocatalytic active material.
 16. Theself-cleaning photocatalytic system of claim 9, wherein the aluminumoxide (Al₂O₃) comprises a θ-Al₂O₃ phase having a crystal structurehaving a monoclinic space group with lattice parameters of a=1.185 nm,b=0.295 nm and c=0.562 nm that enhances lattice matching and formationof the anatase phase of titanium dioxide (TiO₂).
 17. A method ofenhancing photocatalytic activity in a photocatalytic system comprising:depositing a nucleation material coated on a substrate, wherein thenucleation material comprises a metal oxide compound, wherein the metalis selected from the group consisting of: aluminum, zirconium, niobium,cerium, vanadium, lanthanum, titanium, silicon, iron, cobalt, nickel,molybdenum, tungsten, and combinations thereof; and depositing aphotocatalytic active material comprising an anatase phase of titaniumdioxide (TiO₂) over the nucleation material, wherein the nucleationmaterial provides lattice matching to enhance formation of the anatasephase of titanium dioxide (TiO₂), so that a photocatalytic activity isgreater than or equal to about 50% above a comparative photocatalyticactivity where the photocatalytic active material is disposed directlyon the substrate.
 18. The method of claim 17, wherein the depositing ofthe nucleation material is a process selected from the group consistingof: atomic layer deposition (ALD), chemical vapor deposition (CVD),plasma enhanced chemical vapor deposition (CVD), physical vapordeposition (PVD), and combinations thereof.
 19. The method of claim 17,wherein the depositing of the photocatalytic active material is aprocess selected from the group consisting of: atomic layer deposition(ALD), chemical vapor deposition (CVD), atmospheric pressure chemicalvapor deposition (APCVD), low pressure chemical vapor deposition(LPCVD), plasma enhanced chemical vapor deposition (CVD), physical vapordeposition (PVD), magnetron sputtering, wet chemistry, sol-gelprocesses, and combinations thereof.
 20. The method of claim 17, whereinthe depositing of the nucleation material is done by an atomic layerdeposition process and the nucleation material has a thickness of lessthan or equal to about 10 nm.